The present invention relates to a substrate having a first surface and a second surface extending substantially in parallel to the first surface, the substrate being of a material of a first conductivity and provided with a plurality of electrically conducting channels which are extending exclusively in a direction perpendicular to the first and second surfaces, said channels having a second conductivity substantially larger than the first conductivity, the substrate being provided with at least one electrode on either one of the first and second surfaces, contacting at least one of said channels.
Such a device is known from WO-A-96/04585 which discloses an LCD having an active matrix of electronic components, like thin film transistors and thin film diodes, deposited on the outside surface of the LCD cell substrate.
It is to be observed that for the purpose of the present invention, the expression xe2x80x9cexclusively in a direction perpendicular to . . . xe2x80x9d is intended to include deviations inherently due to the production process used. Moreover, the first and second conductivities differ at least by a factor of 1000, but preferably much more, e.g. more than a factor 105.
U.S. Pat. No. 4,613,351 describes a glass material in which parallel conducting tracks are applied in a predetermined direction. The tracks are intended to deflect and detect electromagnetic radiation having a wavelength between less than 0.1 xcexcm and 1 mm.
U.S. Pat. No. 5,438,223 describes a kind of rivet system for interfacial connection of an insulating layer with an electrically conducting material. The electrically conducting parts are applied in holes transversely through the layer and then thermally riveted.
Japanese Patent Application JP-A-081143677 describes the production of a sheet by depositing gaseous material on an electrode. The electrical conductivity in a direction perpendicular to the surface of the sheet is much greater than the electrical conductivity in a direction parallel to the surface of the sheet. However, the conductivity in the direction perpendicular to the surface is in the order of 10xe2x88x926 S/cm, which is very low and in the semiconductor range.
U.S. Pat. No. 5,272,217 describes the use of anisotropic polymers in a sheet. The conductivity parallel to the surface of the sheet of the polymer is much higher than the conductivity in a direction perpendicular to the surface of the sheet. The tetrathiotetracene complex is mentioned as one of the polymers used. Use is made of a xe2x80x9cstack orientationxe2x80x9d in which elements of very small dimensions are grouped head-to-tail.
U.S. Pat. No. 5,556,706 also describes particles of very small dimensions which are oriented head-to-tail in a direction parallel to the surface of a polymer sheet. The sheet is produced by depositing a gaseous material on an electrode. Here, again, there is a greater conduction in a direction parallel to the surface of the sheet than in a direction perpendicular thereto after production.
U.S. Pat. No. 5,229,635 describes a device and a method of orienting very small elements head-to-tail under the influence of an electrical field. Said patent specification is aimed at achieving an electrical conductivity in a predetermined direction parallel to the surface of the sheet. Incident light can be converted into electrical power with the sheet.
Japanese Patent Application 08/007658 describes an adhesive film which is provided with small conducting particles. Prior to use, the film is non-conducting because the conducting particles are not in contact with one another. The film is used to make a connection between the terminal pins of an IC and a substrate. Because the terminal pins of the IC are pressed firmly in the direction of the substrate, electrically conducting connections are produced between the terminal pins of the IC and the conducting particles in the film. As a result of pressing the terminal pins firm enough against the substrate, a conducting connection is produced between the terminal pins and desired electrically conducting tracks on the substrate. At those points where there are no IC terminal pins, the film remains non-conducting. Similar adhesive films are disclosed in U.S. Pat. No. 5,213,715 and Japanese Patent Application 57/111366 and 05/011265.
FIG. 1 shows in a very diagrammatic way the structure of a conventional LCD. The centremost of the three layers shown, indicated by the reference numeral 3, is the optical layer. This is surrounded on either side by two controlling layers 2, 2xe2x80x2. The controlling layers 2, 2xe2x80x2 must be situated as closely as possible to the optical layer 3. In essence, there are two types of optical layers: liquid crystals, which orient themselves under the influence of an electrical field, and light-emitting layers, which emit light under the influence of an electrical current. Light-emitting layers dissipate power during operation, while liquid crystals dissipate energy solely for the purpose of orientation. Light-emitting materials are, for example, LEDs, laser diodes and electroluminescent materials.
Where polarized light is employed, polarization filters are in practice also needed. Said polarization filters and any other correction filters are not described in more detail here because they are not of importance for the present invention. However, where necessary they can in fact be used.
The optical layer 3 generally comprises three layers 4, 6, 4xe2x80x2, as shown in FIG. 2. In addition, supporting layers 1, 1xe2x80x2 are situated on the outside of the controlling layer 2, 2xe2x80x2. The centrally situated layer 6 comprises a liquid-crystal layer in which spacers 5 are situated at regular or irregular distances in order to keep the two insulating layers 4, 4xe2x80x2 at a predetermined distance from one another. The primary function of the layers 4, 4xe2x80x2 is to facilitate the orientation of the liquid crystals in the same direction. Furthermore, they are important in preventing the liquid crystals from being contaminated by migration of ions, such as tin and indium, out of the conductor patterns 2, 2xe2x80x2. Finally, the layers 4, 4xe2x80x2 provide an insulating function.
The controlling layers 2, 2xe2x80x2 comprise, for example, transparent material which contains a pattern of, for example, parallel, likewise transparent conductors. The parallel conductors in the controlling layer 2 are then situated, for example, perpendicular to the transparent, parallel conductors in the controlling layer 2xe2x80x2. Using such patterns, electrical fields can be generated at desired positions transversely or at an angle to the liquid crystal 6 layer, as a result of which the crystals in the liquid crystal layer 6 orient themselves. At the points where this occurs, the liquid crystal layer 6 becomes impenetrable to incident light.
In the conventional structure of an LCD shown in FIG. 2, the controlling layers 2, 2xe2x80x2 are situated inside the supporting layers 1, 1xe2x80x2. Such LCDs can be transported only when the supporting layers have been applied. Without the supporting layers 1, 1xe2x80x2, the LCD structure would be too vulnerable. As a result, it is impossible to make changes and/or corrections in the controlling layers 2, 2xe2x80x2 after the manufacture of the LCD.
In addition, before the controlling layers 2, 2xe2x80x2 have been applied, it is impossible to carry out checks on the correct operation of the liquid crystal layer 6.
Moreover the production yield of LCDs according to the known structure is low. A high percentage, sometimes more than 70%, does not meet the requirements and cannot be sold.
A standard method of orienting the material of the insulating layers 4, 4xe2x80x2 horizontally is the so-called xe2x80x9crubbingxe2x80x9d or frictional treatment. However, because the controlling layers 2, 2xe2x80x2 in the conventional arrangement are applied next to the insulating layers 4, 4xe2x80x2, there is a high risk of damage to said controlling layer 2, 2xe2x80x2 during the rubbing. This arises both as a result of discharge as a consequence of static electricity and as a result of other types of damage.
The controlling layers 2, 2xe2x80x2 are generally composed of indium/tin oxide structures and/or thin-film transistors and/or metal/insulation/metal structures and/or diodes. Polyimide is often used as insulating layer 4, 4xe2x80x2. High temperatures are used during the process for applying the last-mentioned layer, which is an additional hazard for the satisfactory operation of the thin-film transistors, the metal/insulation/metal structures and/or diodes.
The devices disclosed in WO-A-96/04585 referred to above and which are provided with active matrices on the outside surfaces of the LCD cell substrates at least partly solve these problems related to the conventional LCD design. However, still a pattern of individual, transparent electrodes is applied on the inside surface of the LCD cell substrate according to this prior art document. These internal electrodes are connected to the active matrix on the outside of the surface by means of thin conductive leads. Each internal electrode is connected to one single thin conductive lead, whereas each of the thin conductive leads is also connected to one of a series of conductive leads applied to the outside surface of the LCD cell substrate and contacting the active matrix.
No manufacturing details with respect to producing the thin conductive leads in the LCD substrate are given. No other production methods than multi-mask steps vacuum technology in general is referred to. Therefore, the suggested method of producing the devices of WO-A-96104585 necessarily includes extremely difficult alignment steps for properly aligning the thin conductive leads through the LCD substrate with the internal transparent electrodes and the external conductive leads. Especially, it seems difficult if not impossible to transport unfinished LCD""s to a customer without having an active matrix on the outside surface of the LCD substrate and leave it to the customer to apply the active matrix on the outside surface of the LCD substrate in correspondence with his needs. Without undue costs, costumers will not be able to apply their desired active matrix in proper alignment with the thin conductive leads through the substrate.
The primary object of the present invention is to provide a substrate with at least one electrode, the substrate being provided with electrical leads perpendicular to its surface and allowing electrical connection between at least one electrical lead and the electrode without complex alignment procedures.
For this purpose, a substrate of the type mentioned at the outset is characterised in that the at least one electrode has a predetermined minimum dimension in a contact area with the substrate, and that mutual distances between adjacent ones of the plurality of channels are smaller than said minimum dimension of said at least one electrode. Then, no matter where the at least one electrode is contacting the substrate it will always contact at least one of the channels. This greatly reduces alignment problems.
Preferably, the mutual distances are at most two times smaller than the minimum dimension of at least one electrode.
Even more preferably, the mutual distances are at most ten times smaller than the minimum dimension of the at least one electrode.
The plurality of electrically conducting channels may either be distributed in accordance with a regular pattern or randomly through the substrate.
In one embodiment, the mutual distances are smaller than 3.5 xcexcm.
A further object of the invention is to provide a device for displaying information, for example an LCD, which can be transported to customers without the pattern of controlling layers necessarily already having been applied on the substrate and still providing customers with the possibility to apply the pattern of controlling layers on locations desired by them without undue costs and complexity.
A still further object of the invention is to increase the yield of the production of such devices.
To that end, the invention also relates to a device for displaying information, comprising at least:
a first layer which extends in one plane and is composed of a material whose optical properties vary under the influence of an external electrical control system in such a way that either the transparency of portions selected with the electrical control system of the first layer for light incident thereon varies or portions selected with the electrical control system of the first layer emit light;
a second and a third layer which extend substantially parallel to the plane, are situated on either side of the first layer and impart to the device a certain desired rigidity, at least one of the second and third layers being provided with at least one electrode and with electrically conducting channels which are conductive exclusively in a direction perpendicular to the plane, said at least one electrode electrically contacting at least one of said channels,
characterized in that said at least one electrode has a predetermined minimum dimension in the contact area with said at least one of the second and third layers, and that mutual distances between adjacent ones of the plurality of channels are smaller than said minimum dimension of said at least one electrode.
Such a structure has sufficient rigidity to be able to be transported to customers without the ultimately necessary conductor patterns having already been applied. The conductor patterns can be applied by the customer himself on the outside of the second and/or third layer. The conducting channels in the second and/or third layer then ensure that an electrical voltage and/or current whose positions are defined by the pattern of conductors is transmitted to the first layer. The narrower the small channels and the closer together they are situated, the greater the resolution will be.
A further advantage is that, if the pattern of conductors is not correctly applied to the structure thus defined, said pattern can easily be removed without the device as a whole having to be discarded. After removal, the pattern can be applied again. This will appreciably increase the production yield.
The device according to the invention may be a component of an LCD, in which the first layer is a liquid-crystal layer, provided with spacers and in which there is situated between said one of the said second and third layers and the first layer a fourth layer which is made of an electrically insulating material. Said liquid-crystal layer may be of the nematic or smectic type, depending on the desired use. Nematic liquid-crystal layers require a continuous drive in order to be able to have a memory function. This requires suitable electronics, comprising, for example, metal/insulator/metal structures, thin-film transistors, diodes and conductors. Smectic liquid-crystal layers have a spontaneous memory function.
As an alternative, such an LCD may have a polymer dispersed liquid-crystal layer as first layer, a fourth layer which is made of an electrically insulating material being situated between said one of the second and third layers and said first layer.
As a further alternative, the device according to the invention can be designed so that the first layer emits light under the influence of an electric current.
The device according to the main claim of this invention defined in this way and according to the variants mentioned thereof then forms an unfinished plate of material which can subsequently be provided by the user with the necessary application-dependent conductor tracks and electronics. Such an unfinished device can therefore be made as a standard and not in an application-dependent way. This increases the flexibility of the possible applications.
In some applications, not only said one of the second and third layers, but also the other, will have a pattern of electrical conductors which is such that the electrical conductivity of the conductors is directed exclusively in a direction perpendicular to the plane.
In one of the embodiments of the device according to the invention, there is applied to said one of the said second and third layers a photoconducting layer, to the outside of which a transparent electrically conducting layer has been applied. Such a device can be used as electronic paper.
In the case of the device last mentioned, a light source, for example a laser, can be provided to generate a light beam for exposing predetermined locations in the photoconducting layer. Such a device forms a laser-beam display.
The device defined above which is provided with a photoconducting layer to which a transparent, electrically conducting layer has been applied can be used with a laser for manufacturing a mask for photolithographic purposes. The advantage of such a mask is that the locations which are or are not transparent to light can always be defined again without altering the position of the device. Such a mask can therefore advantageously be used in photolithographic processes, because not moving the mask benefits the accuracy.
The device according to the invention can easily be provided with colours on one of the surfaces by applying a photosensitive layer to the side of the device at which the other of the second and third layers is situated. The locations at which the layer has to remain as a coloured layer and those at which it has to be removed can then easily be defined with the aid of exposure procedures and chemical development procedures.
Claims 22 to 26 inclusive define methods for manufacturing a layer of material which extends in one plane and is provided with a pattern of electrical conductors extending exclusively in a direction perpendicular to the surface.